OPEN-LOOP OPTOKINETIC RESPONSES OF THE TURTLE

Turtle eye movements were measured during full-field horizontal optoki netic stimulation under closed and open loop conditions. Because these animals display unyoked slow-phase eye movement behavior, open loop s timulation could not be presented to a paralyzed eye, while monitoring the position of the contralateral eye. The turtle's optokinetic refle x loop was opened electronically by a continuous adjustment of the pat tern's position that effectively canceled the effect of the movement o f the recorded eye. The highest open loop gains (2-3) were observed at low speeds (<1 deg/sec), demonstrating a more limited speed range and lower gain in turtle than in the mammalian optokinetic system. These results in the intact animal can be correlated with the visual respons e properties of the turtle's pretectum and accessory optic system reco rded in vitro. (C) 1997 Elsevier Science Ltd. All rights reserved.